The present invention relates to a power generating technique by an AC/DC converter and, more particularly, to a technique effective to control an output voltage by using a PFC (Power Factor Correction) controller.
For a power supply in an electronic device such as a computer and a server, in recent years, energy saving is an important challenge. For example, to achieve the efficiency specified, particularly, as light load (for example, 20% of the maximum load) in a power saving standard such as Energy Star 4.0 or 80plus, power supply manufacturers make various efforts and spend money.
As a power supply apparatus of this kind, a PFC power supply apparatus is widely known, to satisfy the above-described power saving standard. The PFC power supply apparatus takes a power factor correction (PFC) measure of making current flowing in a commercial power supply close to a sine wave in order to suppress higher harmonic current at the first stage of the power supply apparatus.
Two types of PFC power supply apparatus are known; a PFC power supply apparatus of a passive filter type including an inductance in an input line of the device and smoothing current, and a PFC power supply apparatus of an active filter type of controlling current by using a dedicated PFC controller and a discrete element. Recently, a PFC power supply apparatus of the active filter type which is small and light has become mainstream.
A PFC power supply apparatus of the active filter type includes, for example, a booster converter and a PFC controller. By comparing a feedback voltage amount divided by a voltage feedback resistor that divides output voltage, a current amount detected by a current detecting resistor, and a triangular wave, the on duty of a switching transistor in the converter is controlled to maintain the output voltage constant. The apparatus also performs control of making current flowing in the current detecting resistor, that is, current flowing in so-called AC (alternating current) input close to a sine wave.
The PFC power supply apparatus of the active filter type is classified into: a critical mode PFC power supply apparatus having a mode of detecting that boosted coil current is zero and, after that, switching a switching transistor; and a continuous current mode PFC power supply apparatus for maintaining average current equal to an AC reference signal.